The present invention relates to a soft magnetic alloy and a laminated magnetic core formed by using the same which is used for a transformer, a choke coil, a magnetic head, etc, and in particular to a soft magnetic alloy and a laminated magnetic core having a high heat resistance, a high saturation magnetic flux density and excellent soft magnetic characteristics.
A soft magnetic alloy for use in a magnetic head, a transformer, a choke coil or the like must have the following characteristics:
(1) high magnetic flux density; PA1 (2) high magnetic permeability; PA1 (3) small coercive force: PA1 (4) low magnetostriction; and PA1 (5) a thin shape which can easily be formed. PA1 (6) excellent hardness.
The magnetic head must have the following characteristics in order to improve the wear resistance in addition to the foregoing characteristics (1) to (5):
Therefore, materials for a variety of alloy systems have been studied to satisfy the foregoing characteristics when a soft magnetic alloy or a magnetic head is manufactured. Hitherto, crystalline alloys such as sendust, permalloy and iron-silicon steel and the like have been employed for use in the foregoing purposes. Recently, an Fe-base or Co-base amorphous alloy has been used.
Under the foregoing circumstances, the magnetic head must be adaptable to a magnetic recording medium of a type having large coercive force required to record information at a high density by employing further suitable magnetic material to form the magnetic head that exhibits excellent performance. Further the size of the transformer and the choke coil must be further reduced to be adaptable to the trend of reducing electronic equipment by using a magnetic material having further satisfactory performance.
However, sendust suffers from unsatisfactorily low saturation magnetic flux density of about 11 KG although it has excellent soft magnetic characteristics. Also permalloy encounters a problem of an unsatisfactorily low saturation magnetic flux density of about 8 KG when it is formed into an alloy structure that exhibits excellent soft magnetic characteristics. The iron-silicon steel (Fe--Si Alloy) has a problem of unsatisfactory soft magnetic characteristics although it exhibits a high saturation magnetic flux density.
As for the amorphous alloy, the Co-base alloy has an unsatisfactory saturation magnetic flux density of about 10 KG although it has excellent soft magnetic characteristics. Although the Fe-base alloy exhibits a high saturation magnetic flux density of 15 KG or higher, the attained soft magnetic characteristics are unsatisfactory. The stability of the amorphous alloy against heat is insufficient, resulting in a problem to be solved. Therefore, it is difficult to simultaneously realize the high saturation magnetic flux density and excellent soft magnetic characteristics.
An alloy for a transformer having a high saturation magnetic flux density and exhibiting a low core loss has been disclosed in U.S. Pat. No. 5,069,731, the composition of which is expressed by the following general formula: EQU (Fe.sub.1-a M.sub.1a).sub.100-x-y-z-t CU.sub.x Si.sub.y B.sub.z M.sub.2t
wherein M.sub.1 is Co and/or Ni, M.sub.2 is at least one element selected from a group consisting of Nb, W, Ta, Mo, Zr, Hr and Ti, a, x, y, z and t respectively satisfy, by atom %, 0.ltoreq.a.ltoreq.0.3, 0.1.ltoreq.x.ltoreq.3, 0.ltoreq.y.ltoreq.17, 4.ltoreq.z.ltoreq.17, 10.ltoreq.y+z .ltoreq.28 and 0.1.ltoreq.t.ltoreq.5.
At least 50% of the structure is made of fine crystalline grains and the average grain size obtained by measuring the maximum crystalline grain is 1000 .ANG. or less.
The foregoing fine crystalline alloy has been developed while making a Fe--Si--B amorphous alloy, disclosed in U.S. Pat. No. 5,160,379, as a starting material. In the Fe--Si--B alloy, elements for making the structure to be amorphous are Si and B and the content of Fe in an alloy having sufficient heat stability in terms of practical use is 70 to 80 atom %. The foregoing amorphous alloy has magnetic characteristics superior to that of the conventional Fe--Si alloy (iron-silicon alloy). The fine crystalline alloy disclosed above is a Fe--M.sub.1 --Cu--Si--B--M.sub.3 alloy made by adding Cu and M elements to a Fe--Si--B alloy, where the elements M.sub.3 is at least one element selected from a group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo.
It is necessary for the alloy of the foregoing type to contain Cu because it has been said that the addition of Cu causes fluctuation to occur in the amorphous to generate fine crystalline grains and, accordingly, the structure can be made fine. It has been disclosed in the foregoing application that the omission of the addition of Cu cannot easily produce fine crystalline grains, a compound phase can easily be generated and therefore the magnetic characteristics deteriorate.
In the alloy of the foregoing system, the mutual action between Cu and Nb is able to prevent the enlargement of the crystalline grains. Therefore, it has been considered that composite addition of Nb and Cu is required because sole addition of Nb or Cu cannot prevent the enlargement of the crystalline grains. The foregoing fact has been disclosed by the inventors of the foregoing disclosure in Journal of Materials Transaction, JIM, Vol. 31, No. 4 (1990), pp. 307-314.
FIG. 20 of U.S. Pat. No. 5,160,370, which is a composition diagram, illustrates an important fact that the low magnetostriction cannot be obtained from the alloy of the foregoing system if Si=0. Since Si acts to reduce the magnetostriction, Si must be added to reduce the magnetostriction.
The inventors of the present invention have been developing soft magnetic material by using material of a component system which is completely different from an extremely different viewpoint. Among others, there is a Fe(Co, Ni)--Zr alloy system previously disclosed in U.S. Pat. Nos. 4,623,387 and 4,842,657 established while considering the conventional technologies about sendust, permalloy and iron-silicon steel.
The Fe(Co, Ni)--Zr alloy system contains Zr having excellent performance of forming amorphous added thereto and, accordingly, amorphous alloy can be formed even if the amount of Zr added is reduced. Therefore, the concentration of Fe can be made about 90% or higher. Further, Hf can be used-as an element for forming an amorphous alloy similar to Zr. However, the Curie temperature of the alloy of a type containing Fe at a high concentration is in the vicinity of the room temperature and, therefore, the alloy of the foregoing type is not a practical alloy as the material for the magnetic core.
The inventors of the present invention have found the fact that partial crystallization of Fe--Hf amorphous alloy by a special method enables a fine crystalline structure having an average crystalline grain size of about 10 to 20 nm, and disclosed this in "CONFERENCE ON METALLIC SCIENCE AND TECHNOLOGY BUDAPEST", 1980, pp. 217 to 221. It can be considered from the disclosed technology that fining of the structure of the Fe--M alloy can be enabled even if elements such as Cu are not added. Although the mechanism of this has not been clarified yet, fluctuation of the structure is already present in a rapidly solidified state in a case where the amorphous phase is formed and the fluctuation becomes nucleation site resulting in that a multiplicity of uniform and fine nuclei are generated.
As a result of repeated research on the alloys of the foregoing type, the inventors of the present invention also found that excellent characteristics which cannot be obtained by the Fe--Ma.sub.1 --Cu--Si--B--M.sub.3 alloy disclosed in the foregoing Japanese Paten Publication No. 4-4393 (U.S. Pat. No. 5,160,379) are obtained. Namely, since the Fe--M.sub.1 --Cu--Si--B--M.sub.3 alloy has the property of being abruptly made brittle by heat treatment at 150 to 200.degree. C., the alloy has the drawback that it cannot be applied to a product completed by a process including heat treatment, or including the step of machining without heat treatment and partial heating within the above temperature range, e.g., a transformer produced by cutting an alloy ribbon in appropriate width and length, coiling the cut ribbon and then heat-treating the coil formed, a junction type magnetic head produced through a glass welding step, or a laminate type magnetic head produced by punching an alloy ribbon and then laminating the rings obtained. Further, where a laminated core is manufactured by laser beam machining, there is the problem that the alloy cannot be applied for manufacturing the laminated core by laser beam machining because the alloy is made brittle at a low temperature of 150 to 200.degree. C. The alloy also has the problem that it is unsuitable for warm press working at the above temperature or more.
Although a 50% Ni--Fe permalloy magnetic core or a 80% Ni--Fe permalloy magnetic core is conventionally used as a magnetic core material for the transformer or choke coil, a magnetic core comprising such a magnetic material exhibits a high core loss within a high frequency range, and an abrupt temperature rise within a frequency band of several tens kHz or more, thereby causing difficulty of using the magnetic core.
Therefore, a magnetic core comprising a Co-base amorphous magnetic material has recently been used as a switching power source magnetic core by making use of the characteristics thereof with respect to a low core loss within a high frequency region and high squareness forming properties. However, the Co-base amorphous magnetic core has the problems that it is high cost because of the high material cost, the saturation magnetic flux density is generally 10 kG or less, and the core is susceptible to limit of the operating magnetic flux density within the frequency region of several tens kHz to 100 kHz because of the low saturation magnetic flux density, thereby inhibiting sufficient miniaturization of the magnetic core.
On the other hand, it has been known that a magnetic core comprising an Fe-base amorphous magnetic material exhibits a high saturation magnetic' flux density, a direct current B--H curve having a high squareness ratio and maximum permeability, as disclosed in, for-example, Japanese Patent Publication No. 58-1183.
However, the magnetic core formed by using the Fe-base amorphous alloy has a drawback of high core loss. Although, an attempt is thus made to decrease the core loss by adjusting the elements added, the magnetic core still has the problem of higher core loss than that of the Co-base amorphous alloy.
A first object of the present invention is to provide an excellent Fe-base soft magnetic alloy which has a high saturation magnetic flux density, permeability, mechanical strength and thermal stability, which can resist heat in glass welding, laser beam machining or machining such as cutting or press working, and which can exhibit excellent soft magnetic characteristics after working.
A second object of the present invention is to provide a laminated magnetic core exhibiting a low core loss within a high frequency region and a high saturation magnetic flux density.